This invention relates generally to gate valves and deals more particularly with a gate valve which is capable of being closed in a manner to cut tubing and other suspension members that extend downwardly into a well.
In testing and workover operations performed on oil and gas wells, it is common for wire lines and power cables to be suspended through the wellhead and into the well to support various types of tools and instruments and to supply electrical power to a downhole equipment. It is also common to extend relatively small diameter steel pipe known as "macaroni" tubing into the well to treat the production zones and perform other services. When an emergency arises requiring that the well be immediately shut in, there is usually insufficient time to withdraw the macaroni tubing or the various lines and cables. Consequently, in the event of such an emergency, these suspension members must be cut off in order to quickly shut in the well.
Although the macaroni tubing is normally one inch in diameter or less, it is sometimes considerably larger such as two inches in diameter with a wall thickness of about 1/8 inch. Manifestly, a considerable force is required to shear off pipe of this size. In addition, it is usually necessary to contend with subsea conditions because the emergency situations that require shutting in of the well occur most frequently with subsea wells.